Shitting into a condom then freezing it. Once it is frozen solid, take it out of the condom and use it as a dildo to stick in your lover's ass. Then leave it in until it thaws, then your lover shits it back out and presents it to you "twice baked".

Your sister is hot and so was the twice baked potato she shit onto my chest last night.

Freezing a piece of feces, so it will be hard, like a dildo. The frozen piece of feces is inserted into the sexual partner's anus, like a dildo. This is known as space docking. Once the piece of frozen feces is completely inserted into the anus, it is pooped out onto the other sexual partner. It is a piece of feces that is being pooped twice. Hence the name Twice Baked Potato

Bob took the frozen piece of crap out of the freezer, and put it in Jerry's booty hole. Jerry responded by crapping the crap onto Bob's tits. Jerry turned that space docking into a twice baked potato.

When you fuck someone in the ass, quickly pull out and while the hole is still gaping open, turn around and shit in their ass so they then have to squeeze your turd out of their butt, thereby having the poo "twice baked".